Obsessive-compulsive disorder (OCD) is chronic, debilitating and prevalent, and effective treatments are only now being delineated. Medications with potent serotonin reuptake are only now being delineated. Medications with potent serotonin reuptake blocking effects appear of substantial help to approximately 50% of OCD patients. The investigation drug clomipramine (CMI) is the most extensively studied in clinical trials and was repeatedly found more effective than placebo and other antidepressants. Behavior therapy (BT) involving exposure and response prevention is substantially helpful to about 50% of OCD patients. BT may help patients partially or unresponsive to CMI and may also reduce the high relapse rate reported when the drug is stopped. To date, a conclusive comparison of CMI, BT and their interactive effects has not been done. The specific goals of this proposal are: a) to compare the effects of CMI, BT, CMI+BI and pill placebo for OCD symptoms; and b) to compare the relapse rates for the different groups after discontinuation of treatment. Important to this proposal is the collaboration between pharmacologically and behaviorally-oriented research programs. Each center will enter 76 patients randomized in a 12 week trial with the following groups: CMI alone, BT alone, and CMI + BT, and placebo pill. After week 12, responders will be tapered and/or discontinued from treatments and followed blind to former treatment status for 12 weeks. Medication will be tapered within 3 weeks. Long range goals are to establish guidelines for the mediation and behavioral treatment of OCD cases; to understand the separate and combined effects of drug and BT in this condition; and to integrate pharmacological and psychosocial approaches to the anxiety disorders.